Tramadol is a narcotic, and as far as I understand as long as you aren't taking an NSAID type drug (aspirin, advil, aleve, etc) you won't hurt your crohn's.
If it helps, I have taken Tramadol many many times (I have bad TMJ problems) and it never made me have a flare or anything. I just had to make sure to take it with food or my stomach would hurt really bad, but many medicines (even vitamins) do that to my stomach.
If you are in horrible pain, don't feel bad for wanting relief from it. Take the tramadol if it helps. If it doesn't help, ask to try something different.